1. Field of the Invention
The present invention relates generally to plastic containers; particularly to plastic containers designed to hold liquids under pressure during pasteurization or other thermal treatment.
2. Background Art
Bottles of various configurations and materials have long been employed for the distribution of liquids by the beverage industry. Although the beverage industry traditionally employed glass containers to deliver liquid beverages to customers, that industry has recently embraced the use of plastic bottles due to the relative cost advantages and durability of plastics. For reasons of efficiency and to lower production costs, the plastic container industry has embraced the conventional technique of blow molding plastic containers from plastic preforms. Polyethylene terephthalate ("PET") or polypropylene ("PP") are typically used to construct plastic containers because of, among other reasons, the ability to reclaim and recycle containers constructed therefrom. A barrier layer constructed, for example from ethylene vinyl alcohol ("EVOH"), is sometimes employed with the PET or PP to inhibit the migration of gases such as oxygen and carbon dioxide as well as moisture into or out of, the container.
Although plastic has proven more durable than glass in many aspects, plastic containers may be subject to deformation, in instances in which glass was not, due to the relative strength of thicker glass bottles over the thinner plastic bottles. Sanitation requires that beverages be at least partially sterilized prior to reaching the consumer. Typically this is accomplished by elevating the beverage to a predetermined temperature for a specified period of time in order to kill all objectionable organisms without major chemical alteration of the beverage. The two currently accepted methods for accomplishing such sterilization are hot-filling and pasteurization. Hot-filling entails heating the beverage to the required temperature for the required period of time prior to bottling the beverage. The bottles are then filled and sealed while the beverage remains at an elevated temperature sufficient to assure that living objectionable organisms on the container surfaces are rendered harmless. As the beverage cools from the sterilizing temperature, the internal pressure of the bottle drops and creates a pressure differential with the surrounding environment which is sustained until the bottle is opened by the consumer. Thus, hot-filled bottles often deform inwardly as a result of the pressure differential. This deformation is often referred to as "paneling." Alternatively, the beverage may be sterilized after filling, often referred to in the industry as "pasteurization" and will likewise be so referenced herein. Pasteurzation entails filling each bottle with unsterilized beverage and sealing the bottle. The bottle and its contents are then raised to the desired temperature for the desired period of time in order to kill all objectionable organisms without major chemical alteration of the beverage. Because the beverage is sealed prior to pasteurization, no objectionable organism from the surrounding environment may infiltrate the beverage. The sterility of the beverage is thus guaranteed. The internal pressure of the bottle is substantially elevated with respect to that of the surrounding environment as the pasteurization process heats the beverage in the sealed bottle. This pressure differential may result in outward deformation of the bottle. Although the internal pressure of the bottle typically returns to the pre-pasteurization level, the bottle may retain some deformation experienced during pasteurization.
Prior plastic bottle configurations have attempted to overcome the deformation caused by hot-filling and pasteurization by simply increasing the overall wall thickness of the bottle. The resulting costs and manufacturing difficulties experienced with these configurations rendered them commercially unacceptable. Other bottle configurations have employed various ribs or panels about the bottle in an attempt to elevate its resistance to deformation. However, these configurations created difficulties with properly placing a label on the bottle and the complicated nature of these bottle configurations often rendered the bottle prohibitively costly.
Specific configurations of the bottle base have been constructed to prevent base deformation which may cause the bottle to be unstable when rested upright on its base. One such base configuration can be found in co-pending U.S. patent application Ser. No. 09/172,345 which is hereby incorporated herein by reference in its entirety.
Bottles intended to undergo hot-filling rather than pasteurization are usually designed to absorb the pressure differential that is created by the cooling of the beverage subsequent to sealing the bottle. This pressure absorption is often accomplished by placing "vacuum panels" in the sidewall of a hot-fill bottle. Thus, aesthetic features of hot-fill bottle configurations anticipate, and are designed to accommodate, change resulting from the sterilization process.
Conversely, bottles intended for pasteurization are not designed to anticipate aesthetic changes resulting from the sterilization process. Rather, because the bottle deformation that results from the internal pressure created by pasteurzation subsides once the beverage cools, bottles intended for pasteurization may be molded with the same aesthetic features that will be viewed by the final consumers. Thus, permanent deformation is especially undesirable for bottles intended to undergo pasteurization rather than hot-filling. Permanent deformation resulting from pasteurization is not anticipated. Thus, deformation of pasteurizable bottles should be prevented or, at least, maintained within the elastic zone of deformation for the material from which the bottle is constructed.